How To: Find the GCF

Find the GCF

What Is GCF?

GCF is an acronym for "Greatest Common Factor." GCF is the largest number that can divides evenly into 2 or more numbers.

Step 1:

The first step to finding the GCF is to use what you know about prime factorization. Using a factor tree, find the prime factors of each number. In this example, we will look for the GCF of 12 and 30.

Step 2:

Now that you've found all of the prime factors to both of the numbers, look for all the factors that the two numbers have in common. Then, circle them. In our example, 12 and 30 both have the numbers 2 and 3. Next, multiply all of the factors that the numbers have in common. Using our example, we will multiply 2 and 3, which equals 6. Now we have found that the GCF of 12 and 30 is 6

Practice Time

  1. What is the GCF of 6 and 14?
  1. What is the GCF of 8, 12, and 18?
  1. What is the GCF of 3 and 9?


  1. The GCF of 6 and 14 is 2.
  1. The GCF of 8, 12, and 18 is 2.
  1. The GCF of 3 and 9 is 3.

Step 3:

Practice GCF by playing this game:


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